The use of two dimensional bar codes, which consist of generally rectangular codes with data laid out in an array fashion, has become increasingly popular. Two dimensional bar codes are advantageous because they can hold binary as well as alphanumeric data, and usually include an error correction function. In addition, a two dimensional bar code is significantly more efficient than a traditional one dimensional bar code, being able to store much more information in a smaller space.
DataMatrix is an industry standard two dimensional bar code convention that includes both error detection and correction. Each DataMatrix symbol consists of data regions that contain nominally square modules set out in a rectangular array. A dark module is a binary 1 and a light module is a binary 0. There is no specified minimum or maximum for the X or Y dimension. The data region is surrounded by a finder pattern, a perimeter to the data region that is one module wide, that is surrounded by a quite zone on all four sides of the symbol. Two adjacent sides are solid dark lines used primarily to define physical size, orientation, and symbol distortion. The two opposite sides consist of alternating dark and light modules. These are used primarily to define the cell structure but also assist in determining physical size and distortion. One popular form of DataMatrix symbology is known as ECC 200, which uses Reed-Solomon error correction.
The compact size of the DataMatrix symbols makes them ideal for use in direct part marking. In direct part marking, the DataMatrix symbols are imprinted directly on parts being marked as opposed to being imprinted on labels that are applied to the part. Direct part marking presents challenges caused by the fact that the DataMatrix symbols may not necessarily be imprinted upon a perfectly flat surface or upon a surface with uniform reflectivity properties. In addition, the data modules may be imprinted as circular dots instead of square modules, such as in the case where metallic parts are marked by dot-peening the parts